The present invention pertains to solutions for cleaning silicon semiconductors or silicon oxides. More specifically, the present invention provides solutions which can remove contaminants such as organics, dust and metals from the surfaces of silicon semiconductors and silicon oxides by one step.
Persons in the art continuously engage in modifying the course of production of silicon semiconductor elements and micro-circuits to meet the efficacy and reliability requirements and to provide more reliable processing technology. In the course of production of semiconductor elements, semiconductor wafers and glass wafers are first produced, cleaning steps are conducted thereafter, and then optional operations are conducted. Generally, the modifications of the course of production of semiconductor elements are directed to the cleaning steps. It is believed that the elimination or reduction of contamination on the surfaces of wafers can significantly improve the stability and reliability of elements.
In 1970, RCA (Radio Corporation of America) developed an effective cleaning system for removing contaminants from surfaces of silicon semiconductors and silicon oxides. The system comprises two cleaning steps. An aqueous solution comprising H2O2 and NH4OH is used in the first step to remove organic is used in the first step to remove organic contaminants. Since the solution may inevitably cause contamination with heavy metals such as Fe, Zn and Al which are trace metal contaminants in the solution, a solution containing HCl must be used in the second step to remove the metal contaminants. According to the RCA system, an effective cleaning operation comprises using a solution comprising 5:1:1 to 7:2:1 by volume of H2O/30%H2O2/27%NH4OH in the first step for 10 to 20 minutes and using a solution comprising 6:1:1 to 8:2:1 by volume of H2O/30%H2O2/37%HCl in the second step for 10 to 20 minutes. In other words, RCA system must use strong acid chemicals such HCl, involves two steps and needs at least 20 minutes for cleaning.
Though RCA system can effectively remove heavy metal contaminants from the surfaces of wafers, particles contained in the acidic cleaning solution which comprises HCl will stick to and contaminate the surfaces. Further, RCA system involves two separate steps and this is an inconvenient operation. Persons in semiconductor device and silicon wafer industries continuously search for new formulations to replace RCA system to provide an easier, more effective and more economical cleaning system.
Various approaches have been developed to replace the RCA system and most of them are directed to the cleaning solution of the second step. Japanese Patent KOKAI (Laid-Open) No. Sho 58-30135 discloses the use of an acidic aqueous solution containing HF, H2SO4 and H2O2. Japanese Patent KOKAI (Laid-Open) No. Hei 2-100320 discloses the use of a combination of a mixture of NH4 and H2O2 in water and a mixture of HCl and H2O2 in water. A solution of strong acid and a very small amount of a compound containing fluorine is disclosed in Japanese Patent KOKAI (Laid-Open) No. Hei 4-234118. A solution containing 0.50% HF and 0.1 to 1% H2O2 is disclosed in xe2x80x9cTRYBOROZISTxe2x80x9d Vol. 37, No. 3, (1992) pp. 218-224 and the cleaning is conducted at room temperature. U.S. Pat. No. 5,560,857 discloses the use of an aqueous acidic solution containing 0.005% to 0.05% by weight HF and 0.3% to 20.0% by weight H2O2 and having a pH in the range from 1 to 5. In other words, most modifications on RCA system are directed to the substitution of the solution used in the second cleaning step.
However, as mentioned above, in addition to the shortcoming of particle contamination, RCA system further has the disadvantages of an inconvenient operation (involving two steps and requiring at least 20 minutes) and the use of strong acid chemicals. All the aforementioned known approaches cannot avoid these disadvantages. There is a necessity in the art of an effective cleaning system to simplify the RCA system, avoid the use of strong acid chemicals and meet the simple, effective and economical requirements.
It is an object of the present invention to provide a new cleaning solution which can significantly reduce the cleaning time, simplify the cleaning procedures and avoid the use of strong acid chemicals. Specifically, the present invention provides a solution comprising NH4OH, H2O2 and at least one component A selected from the group consisting of fluoro-containing compounds and other ammonium salts than NH4OH. The solution of the present invention can replace the solutions used in the first and second steps of RCA system and can provide the efficacy of RCA cleaning system by one step.
It is another object of the present invention to provide integrated circuit elements with good electricity appearance and their charge to breakdown and breakdown field are superior to those cleaned by RCA system.